Features like the better stigma system from 4.8 (or was it 4.7, idk), changes to the skill chains and skills in general.
The only classes that are unaffected by the shit skill system are the ones which came in 4.x patches, they were built for comfortable use. Whereas for the old classes, how their skill systems are build is really old and feels like it - uncomfortable. But the stigma system affects all classes, it's doggy poo poo, and for some classes it wastes quite a bit of time when changing stigma builds is required. When changing stigmas, it's like an unnecessary puzzle game, because one must know the prerequisite stigmas to equip the next one for a specific build, which is stupid.
A bit of a rant. I'm just curious if upgrading some features is at all possible.